In a cellular mobile communication system, a relay node (Relay Node: RN) may be provided between an eNodeB (eNB) and user equipment (UE), in order to expand coverage by a cell and/or to attempt to distribute load to the eNodeB (eNB). In this case, the eNodeB functions as a parent eNodeB, and it is referred to as a “donor eNodeB” (Donor eNodeB: DeNB). Here, the donor eNodeB and an eNodeB other than the donor eNodeB may be referred to as the “eNB,” provided that there are no possibilities of confusion. The user equipment (UE) is typically a mobile station. However, the user equipment (UE) may be a fixed station. A radio interface between the eNodeB (eNB) and the relay node (RN) is referred to as “Un.” A radio interface between the relay node (RN) and the user equipment (UE) is referred to as “Uu.”
When a radio link between a relay node (RN) and a donor eNodeB (DeNB) is lost, the radio link is re-established. Based on the items for which the agreements were made in the standardization of the next generation mobile communication system by the third generation partnership project (3GPP) at the time of filing this application, it is defined that, when a radio link failure (Radio Link Failure: RLF) occurs, the radio link is re-established by performing an initial connection procedure (non-patent document 1 disclosed this point).